1. Field of the Invention
The present invention relates to liquid crystal display (LCD) devices and a method for improving color reproducibility thereof, and more particularly to an LCD device and a method for improving a color reproducibility of an LCD device, wherein colors are displayable by the LCD panel by mixing red, green, and blue colors displayable at multiple gray scale levels.
2. Discussion of the Related Art
Flat thin film-type displays express color images, are lightweight, and portable display devices. Liquid crystal display (LCD) devices in particular are capable of displaying pictures at high resolutions, have fast response speeds, and are therefore capable of displaying of moving pictures. Accordingly, research on the design and manufacture of LCD devices is actively performed.
Color LCD devices operate according to anisotropic optical characteristics and polarization properties of liquid crystal molecules. More specifically, alignment directions of liquid crystal molecules with anisotropic optical characteristics can be manipulated to selectively transmit light. Active matrix LCD (AM-LCD) devices display pictures at a high quality and are formed using thin film transistors (TFTs) connected to pixel electrodes arranged in a matrix pattern. A structure of general LCD device will now be described in greater detail.
A related art LCD device generally includes an LCD panel having a color filter panel and an opposing TFT array panel both formed of transparent substrate material. The color filter and TFT array panels are disposed a predetermined distance from each other to define a cell gap. A layer of liquid crystal material is formed within the cell gap. The color filter panel supports red, green, and blue color filters sequentially arranged at positions corresponding to the pixel electrodes, a black matrix having a net-type shape formed between the color filters, and a common electrode formed on the color filters. The TFT array panel supports pixel electrodes arranged at pixel positions provided in a matrix pattern, gate lines formed along a horizontal direction of the pixel electrodes, data lines formed along a vertical direction of the pixel electrodes, and TFTs for driving the pixel electrodes formed at sides of the pixel electrodes. Each TFT includes a gate electrode connected to the corresponding gate line and a source electrode connected to the corresponding data line. Moreover, pad units, formed at ends of the gate and data lines, are used to connect the TFTs to external driving circuits.
FIG. 1 illustrates a schematic view of a related art liquid crystal display panel and a related art driving unit.
Referring to FIG. 1, red (R), green (G), and blue (B) image information (DATA) and control signals (CS) are applied to a timing control unit 120 via an interface unit 110. A system power (VCC) is applied to the timing control unit 120 and a power unit 130.
The timing control unit 120 applies the control signal (CS) to a gate driving unit 140 and applies the image information (DATA) and the control signal (CS) to a data driving unit 150. The control signal (CS) includes a clock signal, a gate start signal, and a timing signal and enables the timing control unit 120 to control a driving timing of the gate and data driving units 140 and 150.
The power unit 130 receives the system power (VCC), applies gate on/off power (VG-ON, VG-OFF) to the gate driving unit 140, applies a reference voltage (VREF) to the data driving unit 150, and applies a common voltage (VCOM) to the common electrode of the LCD panel 100.
The gate driving unit 140 receives the control signal (CS) applied by the timing control unit 120 and the gate on/off power (VG-ON, VG-OFF) applied by the power unit 130 and applies scan signals to the gate lines of the LCD panel 100.
The data driving unit 150 receives the control signal (CS) and the image information (DATA) applied by the timing control unit 120 and the reference voltage (VREF) applied by the power unit 130 and applies the image information (DATA) to the data lines of the LCD panel 100.
Pixels in the LCD panel 100 are arranged in a matrix pattern and express light of predetermined colors in accordance with the applied image information (DATA), applied by the data driving unit 150 in accordance with the scan signals applied by the gate driving unit 140. R, G, and B image information (DATA) are applied to corresponding ones of R, G, and B pixels, wherein R, G, and B pixels constitute one dot within a display area of LCD panel 100. By combining light expressed by the R, G, and B pixels, predetermined colors may be displayed by the LCD panel 100.
To display natural-type colors, R, G, and B colors must be expressed by the LCD panel 100 at multiple gray scale levels. For example, when R, G, and B colors (i.e., the three primary colors primary colors) are expressed by the LCD panel 100 without using gray scale levels, only 23 (i.e., 8) colors (black, red, green, blue, white, red+green, green+blue, and blue+red) are expressable by a dot of the LCD panel 100. However, when R, G, and B colors are expressed by the LCD panel 100 at an 8-bit gray scale level, 224 (i.e., 16,777,216) colors are expressable by a dot of the LCD panel 100. Accordingly, R, G, and B colors expressable using multiple gray scale levels can be mixed together to generate natural colors.
FIG. 2 illustrates an X-Y chromaticity diagram, quantitatively illustrating natural colors.
Referring to FIG. 2, the color and degree of color saturation can be uniquely described according to the X-Y coordinates of the chromaticity diagram. Light having chromatic values on and within the closed, horseshoe-shaped region C-100 is viewable by humans. Light having chromatic values within the triangular region T-100 defined by “R,” “G,” and “B” vertices is displayable using an NTSC fluorescent lamp. Accordingly, light within the triangular region T-100 may express color that is reproducible. Light having chromatic values defined by the R1, G1, and B1 distributions are expressed as red, green, and blue colors, respectively, and are displayable by the LCD panel 100 at multiple gray scale levels.
More specifically, when the gray scale level of light having a red color displayed by the related art LCD device is increased, in the chromaticity diagram, the R1 distribution is generated. When the gray scale level of light having a green color displayed by the related art LCD device is increased, in the chromaticity diagram, the G1 distribution is generated. When the gray scale level of light having a blue color displayed by the related art LCD device is increased, in the chromaticity diagram, the B1 distribution is generated.
As the gray scale level of the blue color displayed by the related art LCD device increases, the end portion of the B1 distribution deviates along the Y-axis, away from the “B” vertex of the color reproduction region T-100. Accordingly, as the gray scale level of light having a blue color displayed by the related art LCD device increases, the degree to which the blue color is reproducible decreases. The phenomenon by which the color reproducibility is decreased upon increasing the gray scale level of light having the blue color will now be described in greater detail below.
FIG. 3 illustrates a graph of a Gooch-Tarry curve, indicating a difference in transmissivity of R, G, and B colors through the cell gap of the LCD device.
R, G, B colors have different wavelengths within a visible wavelength region. Similarly, and with reference to FIG. 3, R, G, and B colors are transmitted by the LCD device according to the cell gap and a refractive index of the liquid crystal material provided within the cell gap. Accordingly, distortion of colors expressed by the LCD device may occur. For example, transmissivity characteristics of light having blue color are reduced when transmitted through a normal cell gap. Accordingly, the gray scale level of the blue color must be increased. However, as the gray scale level of the blue color increases, the end of the B1 distribution undesirably deviates along the Y-axis, away from the “B” vertex of the color reproduction region T-100 shown in FIG. 2.
Therefore, within the related art LCD device, color reproducibility of light having blue color decreases as the gray scale level of the blue color displayed by the related art LCD device increases. Due to the aforementioned transmissivity and reproducibility characteristics of light having the blue color, the quality with which the LCD device displays pictures is lowered and the overall desirability of the LCD device may be reduced.